1. Technique Field
The present invention relates to a wire electric discharge machining apparatus for machining a workpiece by causing electric discharge in a gap (hereafter referred to as “work gap”) formed between a wire electrode and the workpiece. In particular, the present invention relates to a wire electric discharge machining apparatus in which machining conditions can be varied.
2. Background Technique
In general, a wire electric discharge machining apparatus has a wire electrode supported vertically between a pair of wire guides. During machining, the wire electrode is unwound from a bobbin, and travels along a transport path. Dielectric fluid is injected into the work gap during machining. Dielectric fluid may be water having a resistivity of 5×104-1×105 Ω·cm. A wire electric discharge machining apparatus applies voltage pulses to the work gap in order to cause electric discharge. Dielectric fluid is ionized by the application of voltage, and electric discharge occurs in the work gap.
As a result, current flows through the work gap and an on-time commences. On-time is also called pulse duration. When on-time is completed, the wire electric discharge machining apparatus stops supply of current and an off-time is commenced. Off-time is also called pause time. When off-time is completed, the wire electric discharge machining apparatus again applies voltage to the work gap. Supply of current pulses to the work gap is then repeated, and workpiece material is removed.
Machining conditions are determined based on material and thickness of the workpiece, and diameter and material of the wire electrode. Machining conditions are also based on a target value for surface roughness. Machining conditions include, for example, on-time and off-time of current pulse, travel speed and tension of the wire electrode, and pressure of the dielectric fluid. Japanese Patent No. 2688128 discloses a wire electric discharge machining apparatus that varies machining conditions when workpiece thickness varies.